The present invention relates to power supplies for delivering DC voltages which are useful for normal electronic equipment such as voltages in the order of 10-40 Volts. The power supply concerned includes a MOS-FET transistor circuit arrangement operating as a DC/DC converter. Such power supplies are for instance described in MOS Power Applications Handbook from Siliconix TK 7821.95.M67 1984, but they are not suitable for being energized with voltages lower than 5 Volts.
The characteristic features of a MOS-FET transistor are that it has a very low internal resistance in the on-condition (a drain-source resistance &lt;15 milliohms). When the term MOS-FET is used in the present specification and claims, it includes all types of transistors having such characteristics.
Power supplies operating from voltages lower than 5 Volts may have many applications in portable equipment and in other apparatus in areas where ordinary power lines are not available. When the power generation is based on supply of voltage from a sea or salt water galvanic cell, possible user groups and applications are: rescue equipment, privately owned boats and yachts, off-shore industry, fishing industry, lighthouse services, meteorology, naval defense, telecommunication.
Salt water galvanic cells are known from for instance U.S. Pat. No. 3,401,063. This patent mentions that DC/DC or DC/AC converters, known from U.S. Pat. Nos. 2,849,615 and 2,987,665, are suitable for producing a desired voltage output. Experiments have, however, shown that the efficiency of these converters is very low.
The main object of the present invention is in general to provide power supplies which are more efficient than known power supplies. The object of the invention is in particular to provide efficient power supplies which include use of sea water galvanic cells.
There are several features that are required from a power supply which is to be used in sea water.
The converter must start functioning when its input voltage rises to a valve corresponding to the low voltages usually delivered by a sea water galvanic cell, i.e. voltages lower than 5 Volts, usually lower than 0.6 Volt. PA1 It should preferably not be necessary to use any auxiliary voltage source to start the converter. In some applications, it would, however, be desirable to have this possibility. PA1 The converter should have the highest possible efficiency. PA1 The converter should preferably be voltage controlled. This means that when the load does not require any current, the converter should draw the least possible current from the low voltage source. PA1 The converter should be capable of withstanding rough handling and tough environments like salt water, water pressure and so on according to specifications. PA1 The converter should have a simple construction in order to obtain a high MTBF. PA1 The converter should be able to withstand shortcircuits on the output or reversed polarity of the input terminals. PA1 The converter should also have the possibility of being current controlled. This means that the converter should be able to deliver substantially constant current independent of load and input voltage. PA1 The converter must be capable of being stopped or started with predetermined external signals. PA1 The converter must be capable of being constructed by modules which may be interconnected to provide increased output. PA1 light and emergency radiotransmitters on lifevest and liferafts PA1 float free beacons PA1 dynamic positioning devices PA1 hydro-accoustic transmitters PA1 pressure and temperature sensors in offshore installations PA1 seismic measuring devices PA1 net indicator lights on fishing equipment PA1 buoys with sensors and radiotransmitters for meteorological purposes. PA1 It may in many instances substitute oil and gas supplies which are used for running lighthouses, lights and lanterns. Furtermore, it may be used to supply on site power for submarine detection and alarm systems and for fiber optic repeater stations. Such subseas installations are now supplied with electrical power from the mainland, from an oil rig, or in some cases power is achieved by using some type of dry cells which needs relatively frequent and costly replacement. PA1 Indefinite storage PA1 Long life PA1 high level of reliability PA1 compatibility with existing equipment PA1 ease of installing PA1 low maintenance costs (the cell only is replaced) PA1 low initial costs.
Most of these requirements are valid for any application of the power supply.